Until recently, it was believed that the primary function of white brain matter was to insulate nerve fibres, but new research strongly indicates that white matter also plays an important role in memory and learning. The findings are reported in a paper published in the latest issue of Science by a team led by Ragnhildur Þóra Káradóttir, professor in Cellular Neuroscience at the University of Cambridge and professor of Neurophysiology at the University of Iceland’s Faculty of Medicine. She explains that this new information could potentially change the way we think about brain function relating to learning and memory and help identify ways to prevent memory loss.
Ragnhildur's co-authors were Giulia Bonetto and David Belin, her colleagues at the University of Cambridge. The paper is an invited review article, summarising the latest research on white brain matter, or myelin, a subject that has received little attention until recently.
The nervous system is made up of white and grey matter. White matter in the nervous system consists of myelin and represents about half the total weight of the body. White matter is found inside grey matter in the brain, but also in the spine and nerves throughout the body.
Myelin forms a kind of sheath or coating over axons. Myelin helps nerve impulses to be transmitted rapidly around the body, between neurons and to other kinds of cell, e.g. from the brain and spine to muscle cells when we move. Myelin therefore plays a vital role in the nervous system and diseases such as MS and cerebral palsy can be attributed to a lack of or damage to myelin sheaths.
We know that the brain responds to changes and stimuli in the environment, enabling organisms to learn and remember and change behaviour accordingly. In response to external stimuli, certain neural networks are formed in the brain. Neural pathways in the brain are then strengthened through repetition, for example when a child learns to talk or walk. However, there is a lot about this complex process that remains a mystery. Research has previously focused almost exclusively on how the learning affects synapses.
"This research has been overlooked so far, but the studies suggest, for example, that if new myelin is not formed when we learn something, we will forget what we learned. Everything we know indicates that myelin is essential to remembering what we learn. We are just starting to understand the function of myelin in the nervous system and this new information could potentially change the way we think about how the brain works and about learning and memory."
The authors of the paper report that there has been little attention given to the role of myelin and myelin sheaths in these processes. Myelin has been thought of primarily as insulation for axons. But new research, described in the review article, suggests that myelin sheaths in the brain change when we learn something new and that this affects neural pathways and systems in the brain relating to learning and memory. However, further research is required to clarify these relationships.
"This research has been overlooked so far, but the studies suggest, for example, that if new myelin is not formed when we learn something, we will forget what we learned. Everything we know indicates that myelin is essential to remembering what we learn. We are just starting to understand the function of myelin in the nervous system and this new information could potentially change the way we think about how the brain works and about learning and memory," says Ragnhildur, who has many years of experience researching a a cell called oligodendrocytes, which produce myelin in the central nervous system.
She adds that better understanding of the function of myelin and its role in learning and memory could also advance knowledge of various diseases related to the brain. "Increased knowledge in this area could help us find ways to prevent the memory loss associated with various kinds of dementia."